Rubber composition and preservation of rubber



Patented Dec. 1, 1936 PATENT OFFICE RUBBER COMPOSITION AND PRESERVA- TION OF RUBBER Joseph B. Ingram, Nitro, W. Va., assignor, by

mesne assignments, Company, St. Louis, Delaware to Monsanto Chemical 7 Mo., a corporation of No Drawing. Application October 28, 1933, Serial No. 695.720

8 Claims.

The present invention relates to the art of rubber manufacture, and particularly relates to the preparation of rubber compositions which resist deterioration due to aging or to exposure to the atmosphere. It has long been known that such deterioration can be greatly retarded by treating the rubber either before or after vulcanization with certain substances known as ageresisters or antioxidants. One object of this invention is to provide a new and, superior class of antioxidants for rubber. A further object of this invention is to provide a new and superior class of materials which when incorporated into rubber, preferably before the vulcanization thereof, imparts thereto properties markedly resistant to tear and cracking when portions thereof have been repeatedly and alternately stretched and the tension removed. Such a process is analogous to the flexing of an automobile tire in actual road service.

The age resisting characteristics of a vulcanized rubber product can be readily ascertained by subjecting samples of the vulcanized product in a bomb to the action of oxygen under elevated pressure and at an elevated temperature. The aged rubber samples are then examined and tested and the test data compared with the results obtained on testing the unaged rubber samples. The deterioration in properties eflected as a result of the oxidation treatment is indicative of the result that would normally be expected of that particular stock dur-' Y ing actual service. Such a test is known as the Bierer-Davis aging test and produces an effect on a vulcanized rubber stock comparable with that resulting from'several years of natural aging of the rubber depending upon the condi tion of the test. In all the tests hereinafter set forth, the aging was carried out at temperatures of 70 C. and an oxygen pressure of 300 pounds per square inch.

The flex cracking resistance of the vulcanized rubber products was determined on a flexing machine as set forth by L. V. Cooper, Analytical Edition of Industrial and Engineering Chemistry, vol. 2, No. 4, 1930, pages 391-394.

According to the present invention, a new class of antioxidants or age-resisters has been found which, upon incorporating into a rubber stock, imparts exceptional age resisting qualities'and flex cracking resistance to the vulcanized rubber product. The compounds herein disclosed as imparting such desirable properties to vulcanized rubber comprise the reaction products of 8. mono primary amino diphenyl and a ketone,

For example, the following reaction products are typical members of the preferred class of materials outlined above: reaction products of ortho amino diphenyl, para amino diphenyl, mixtures of ortho amino diphenyl and para amino diphenyl, for example a mixture of substantially 45% ortho amino diphenyl and 55% para amino diphenyl respectively, with acetone, methyl ethyl ketone, diacetone alcohol, mesityl oxide, phorone, di-isopropyl ketone, isobutyl 10 methyl ketone, acetophenone and benzophenone.

Any one or a mixture of the above enumerated substances or of these substances with other antioxidants may be incorporated into rubber with good effect on its age resisting qualities and 5 flex cracking resistance thereof.

The following are to be understood as illustrative of the invention and not limitative of the scope thereof.

Example I parts by weight of para amino diphenyl and 166 parts by weight of acetone were placed in a suitable reactor and heated under positive pressure in the presence of a suitable catalyst or condensing agent, for example 1.88 parts by weight of bromine, for eighteen hours at a temperature of substantially 1'70 to 180 C. At the end of this period the water produced by the reaction and any unreacted acetone and para amino diphenyl were removed from the reaction mass preferably by distillation. The residue comprising the, preferred reaction product was incorporated in the usual manner in a rubber The rubber stock thus compounded was vulcanized in the well known manner and portions of the vulcanized product were then artificially aged by heating in a bomb for 48 hours at a ternperature of C. and under a pressure of 300 pounds of oxygen per square inch. A comparison 5 betweentheagedandunaged-rubberproductis given-in'lableL' Table I a museum ran. at am inibs/ln Mine.

am not sent m m assess H i The data set forth in Table I shows that the pre ferred class of materials. for example, the reaction product of acetone and para amino diphenyl.

comprise an important group of antioxidants.

If convenient or desirable a smaller ratio of ketone to amine may be employed than that set forth above. Thus, acetone and para amino diphenyl in the ratio of substantially two molecular proportions of the former to substantially one molecular proportion of the latter have been reacted by heating under positive pressure at a temperature of substantially 1'10 to 180 C. for substantially 20 hours. The water formed by the reaction and any unreacted acetone or para amino dlphenyl were removed from the reaction product preferably by distillation. The resulting crude reaction product was distilled at reduced a pressure. and a liquid distilling at 180 to 240' C.

under 4 mm. pressure of mercury. thereby obtained. The material so obtained was incorporated in a typical tread stock comprising Parts 40 Smoked sheet rubber 100 Carbon black 50 zinc oxide 5 Sulfur 3 Pine tar--- 2 as Stearic acid- 3 Reaction product of benzoyl chloride and the sodium salt of mercaptobensothiasole 0.8 Diphenyl guanidine 0.2

so Reaction product of para amino diphenyl and acetone 1.0

The rubber stock so compounded after vulcanixing,onagingintheoxygenbombinthe manner hereinbefore set forth. was found to possess most desirable antioxidant properties. Furthermore. upon flexing the cured rubber stock in the manner described above, it was found to 838M916 II 1 parts by weight (0.38 mol.) of a mixture of substantially 55% para amino dlphenyi and substantially 45% ortho amino diphenyl and 44 parts by weight (0.76 moi.) of acetone were placed in asuitable reactor equipped with a reflux air 1 condenser to which was a water cool d oondenseraopositionedastocondenssbutnot returntothereactoranyunreactedacetona, 1.5 partsbyweightofasuitablecatalystorcondens ing agent, for example bromine. were added thereto. Themixtureoforthoandparaamino s diphenyl, acetone and catalyst was'heatedtosub-. stantially 150-155' C. and an additional amount ofacetonecomprisingmpartsbyweightadded slowly thereto by means of a dropping funnel extending below the surface of the liquid over 10 a period of substantially six hours.-

reaction mixture was then dissolved in a suitable sol-'- vent. for example benzene, and the solution extracted with a dilute acid, for example 5% hydrochloric acid, in order to eliminate any unreacted amino diphenyl. The solution, after extracting with hydrochloric acid, was washed first with waterandthen withanslkaliforexamplea5% aqueous caustic soda solution until neutral, dried with a suitable dehydrating agent as for example anhydrous sodium sulfate, and the solvent removed preferably by distillation. The residual product comprising a viscous liquid was incorporated in the usual manner in a rubber tread stock comprising I Reaction product of acetone and a mixv tureoforthoandparaaminodiphenyl 1.0

The compounded rubber stock was vulcanised 40 and the vulcanised rubber product found to possees the typical desirable aging qualities of the preferred class of materials. 'lhe cured rubber product containing the reaction product of acetone-andthemixtm'eofsubstantiallyiiilqt para 5 amino diphenvl and ortho amino diphenyl wasalsofoundontestinginthemannerhereinbefore set forth to be markedly superior in flex cracking resistance over a similar stock containingnoneofthenewandpreferredclassof 5o materials.

From the specific examples hereinbefore set forth. it is shown that rubber compositicms containingsmallproportionsofthepreferredciass' of materials markedly resist the deterioration iniiuences due to heat, oxidation and flexing.

Obviously. practice of the present invention is not limited to the specific compositions given above. such compositions being merely illustrative of the manner of employing the'antioxidants or so age-resisters of this invention. The antioxidants or age-reststers may be employed in conjunc- .tionwithothervulcanisingagentsthanthose specifically disclosed. for this invention is applicable generally to pure rubber or rubber comg positions of the most varied nature. Furthermore, the preferred class of materials may be employed in rubber stocks in conjunction with other accelerators than the one specifically shown with varying differences in tensile and modulus properties but still exhibiting the desirable quailties of the class.

Itisto beunderstoodthatthetermtreating" asmnployedin theappended claimsisusedina generic scnsetoinciudeeitherthefnoorporating 7s of crude or vulcanized rubber.

proportions of acetone at a temperature of subofthe preferred class of materials into the rubber by milling or similar process, or their addition to the rubber latex before its coagulation, or to the application thereof to the surface of a mass The term rubher" is likewise employed in the claims in a generic sense to include caoutchouc, whether natural or synthetic, reclaimed rubber, balata, gutta percha, rubber isomers and like products whether or not admixed with fillers, pigments or accelerating agents.

The present invention is limited solely by the claims attached hereto as part of the present specification.

What is claimed is:

1. The method oi. preserving rubber which comprises treating rubber with a reaction product obtainable by reacting para amino diphenyl with acetone.

2. The method of preserving rubber which comprises treating rubber with a reaction product obtainable by heating in the presence of a halogen condensation catalyst under pressure substantially one molecular proportion of para amino diphenyl with substantially two molecular proportions of acetone at a temperature of substantially to C. V

3. The method of preserving rubber which comprises treating rubber with a reaction product obtainable by heating in the presence of a halogen condensation catalyst under pressure substantially one molecular proportion of para amino diphenyl with substantially two molecular stantially 170 to 180 C. and having a distilling range of substantially 180 to 240 C. at 4 mm. pressure of mercury.

4. The method of preserving rubber which comprises treating rubber with a reaction product obtainable by reacting para amino diphenyl with an aliphatic ketone containing more than two but less than ten carbon atoms.

5. The method of preserving rubber which comprises treating rubber with a reaction product obtainable by passing acetone continuously into para amino diphenyl heated to liquid temperature in the presence of an acidic condensation catalyst.

6. The vulcanized rubber product prepared by heating rubber and sulfur in the presence of a reaction product obtainable by reacting para amino diphenyl with an aliphatic ketone containing more than two but less than ten carbon atoms.

7. The method of preserving rubber which comprises treating rubber ,with a reaction product obtainable by reacting para amino diphenyl with one member of a group consisting in acetone, methyl ethyl ketone, diacetone alcohol,

1 mesityl oxide, phorone, di-isopropyl ketone and isobutyl methyl ketone.

8. The vulcanized rubber product prepared by heating rubber and sulfur in the presence of a reaction product obtaintable by reacting para amino diphenyl with acetone.

JOSEPH R. INGRAM.

CE RTIFIGATE OF CORRECTION.

Patent No. 2,052,885. December 1, 1936 JOSEPH R. INGRAM.

It is hereby certiiiefthat error appears in the printed specification of r the above numbered patent requiring correction as follows: Page 1, second column, line 43, for "benzol" read benzoyl; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office. Y

Signed and sealed this 16th day of February, A. D. 1937.

Henry Van Arsdale (Seal) Acting Commissioner of Patents.

of crude or vulcanized rubber.

proportions of acetone at a temperature of subofthe preferred class of materials into the rubber by milling or similar process, or their addition to the rubber latex before its coagulation, or to the application thereof to the surface of a mass The term rubher" is likewise employed in the claims in a generic sense to include caoutchouc, whether natural or synthetic, reclaimed rubber, balata, gutta percha, rubber isomers and like products whether or not admixed with fillers, pigments or accelerating agents.

The present invention is limited solely by the claims attached hereto as part of the present specification.

What is claimed is:

1. The method oi. preserving rubber which comprises treating rubber with a reaction product obtainable by reacting para amino diphenyl with acetone.

2. The method of preserving rubber which comprises treating rubber with a reaction product obtainable by heating in the presence of a halogen condensation catalyst under pressure substantially one molecular proportion of para amino diphenyl with substantially two molecular proportions of acetone at a temperature of substantially to C. V

3. The method of preserving rubber which comprises treating rubber with a reaction product obtainable by heating in the presence of a halogen condensation catalyst under pressure substantially one molecular proportion of para amino diphenyl with substantially two molecular stantially 170 to 180 C. and having a distilling range of substantially 180 to 240 C. at 4 mm. pressure of mercury.

4. The method of preserving rubber which comprises treating rubber with a reaction product obtainable by reacting para amino diphenyl with an aliphatic ketone containing more than two but less than ten carbon atoms.

5. The method of preserving rubber which comprises treating rubber with a reaction product obtainable by passing acetone continuously into para amino diphenyl heated to liquid temperature in the presence of an acidic condensation catalyst.

6. The vulcanized rubber product prepared by heating rubber and sulfur in the presence of a reaction product obtainable by reacting para amino diphenyl with an aliphatic ketone containing more than two but less than ten carbon atoms.

7. The method of preserving rubber which comprises treating rubber ,with a reaction product obtainable by reacting para amino diphenyl with one member of a group consisting in acetone, methyl ethyl ketone, diacetone alcohol,

1 mesityl oxide, phorone, di-isopropyl ketone and isobutyl methyl ketone.

8. The vulcanized rubber product prepared by heating rubber and sulfur in the presence of a reaction product obtaintable by reacting para amino diphenyl with acetone.

JOSEPH R. INGRAM.

CE RTIFIGATE OF CORRECTION.

Patent No. 2,052,885. December 1, 1936 JOSEPH R. INGRAM.

It is hereby certiiiefthat error appears in the printed specification of r the above numbered patent requiring correction as follows: Page 1, second column, line 43, for "benzol" read benzoyl; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office. Y

Signed and sealed this 16th day of February, A. D. 1937.

Henry Van Arsdale (Seal) Acting Commissioner of Patents. 

